JPS59154599A - Fine signal measuring apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the measurement of minute signals, and is particularly suitable for low-cost, high-precision detection devices required for automotive electronic equipment. More specifically, when a minute signal is detected and amplified, it is attempted to automatically remove it using a simple means of off-cell technology that exists in the output of the amplifier, and constantly removes the effects of manufacturing variations or temperature characteristics of the amplifier. It is an attempt to provide accurate information.

An example of automotive equipment that requires this type of minute signal measuring device is a device that detects the temperature of an exhaust gas purification catalyst and warns or suppresses excessive temperature rise. In currently known three-way catalysts, 800
C. to 900.degree. C. is considered to be the high temperature limit, but on the other hand, the economic efficiency of catalysts forces operation close to the limit temperature. For this reason, a thermocouple is installed inside the catalyst or the catalyst case to constantly monitor the entire temperature and to give a warning to the driver of the vehicle when the temperature reaches a critical temperature. Thermocouples are suitable for high temperature measurements, but the disadvantage is that the output is very small and pressure; for example, the CA type has an extremely small output of 49 mV at 1200°C, or 41 μV/°C. All occur. On the other hand, an amplifier that receives this minute signal and amplifies the voltage has an input offset voltage of several mV, typically about 5 mV, unless a particularly expensive high-precision amplifier is used. When this offset is calculated into temperature, it becomes 5mV/41 ttV/°C=122°C. As mentioned above, in order to protect the exhaust gas purification catalyst whose temperature rise approaches the limit temperature, the temperature error due to this offset is unacceptable.

Therefore, adjustment of the offset voltage has been conventionally performed. The conventional device will be explained below with reference to the drawings.

Figure 1 shows a typical example of a conventional device, where 1 is an exhaust gas purification catalyst, 2 is a thermocouple installed in the exhaust gas purification catalyst, 3 is a measuring device, and 4 is an amplifier with a thermocouple at its (+) terminal. One terminal of 2 is connected via a resistor 5. 6 and 7 are resistors for setting the amplification factor. 8 and 9 are resistors, which are connected together with a variable resistor lO so as to superimpose the voltage obtained by dividing the voltages of 1E and -E into the (-) terminal of the amplifier 4. 11 is an A/D which converts the output 'eA/D of the amplifier 4 and provides a digitalized voltage signal to the CPU 12.
It is a converter. Reference numeral 13 is the output of the CPU 12, which operates all the objects to be controlled by this measuring device. 14 and 15 are connecting terminals between the thermocouple 2 and the measuring device 3.

Now, the output VO of the amplifier 4 is as follows.

7 Vo=(VI+VO8)K-ES・-8 7=VIK+ (VosK-ES・□) 8 where R6 to RIO are the resistance values of resistors 6 to 10, respectively. Further, vI is the output voltage of the thermocouple 2, and Vos is the input equivalent offset voltage of the amplifier 4. As is clear from the above equation, the resistance value Rro' of the ks k variable resistor 10
By adjusting fr and setting it to an appropriate value, it is possible to set 7VQ5K -E5- = 0. At s, it is possible to obtain the relationship V□ = VIK, which is proportional to the true output of thermocouple 2. An output normal pressure Vo is obtained.

However, adjusting the offset voltage using the variable resistor 10 as described above has the following drawbacks. Firstly,
Since the offset voltage VO3 has a dependence on temperature, it cannot be said that it is suitable for adjusting the offset voltage within a wide operating temperature range required for automotive electronic equipment. Second, the adjustment of vI4 of the variable resistor 10 is not suitable for mass production, and there is also concern about deviations in the adjustment value caused by vibrations of the automobile.

The present invention has been made to eliminate the above-mentioned drawbacks of the conventional device, and can completely and automatically remove the offset voltage of the amplifier, making it possible to accurately measure minute voltages. The purpose is to provide a microvoltage measuring device that can measure small voltages.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 2, 16 is a measuring device, 17.18 is an analog switch, 19 is a resistor, 20.21 is the r-) signal line of the analog switch 17.18, and the r-t signal is supplied from the CPU 12. .

Other configurations are the same as before.

In the above device, the output of the thermocouple 2 is connected to the (+) terminal of the amplifier 4 via the analog switch 17 and the resistor 5. connected to a connection point. Analog switch 17.18 from CPU12
The dirt signal given to analog switch 17.18
'i Control opening and closing in opposite ways.

In the first state where the analog switch 17 is on and the analog switch 18 is off (well, the output voltage VI of the thermocouple 2 is given to the amplifier 4, and the output voltage V of the amplifier 4 is
O is V□ = (Vr + Vos) K ・
---11 + this output voltage vO is A/D converter 11
After conversion, the data is read by the CPU 12.

Next, analog switch 17 shuts off, analog switch 1
In the second state where 8 is conductive (1, the output type H2 of thermocouple 2 is released and zero is input to amplifier 4. Corresponds to the case, vo= vo sK ・−・
・It is expressed as -+21. This output voltage? O is also C
It is read by PU12.

Next, the operation of the CPU 12 will be explained using the functional blocks shown in FIG. In FIG. 3, 22 and 23 are memories which are controlled by a control block 25 to store all the diisotal signals corresponding to the tl1 equation and the equation (2), respectively. This control is performed in synchronization with each gate signal as shown. That is, the memory 22 updates the stored contents in the J-th state, and retains all stored contents in other states. Also, the memory 23 updates the memory contents at the 20th state,
In other states, the memory contents are retained. The contents A and B of the memories 22 and 23 are respectively A= (VI +Vos)
K%B = VO8K. Therefore, if each memory 22°230 output A, B is subtracted by the subtracter 24, A - B = (VI + VO8) K - VosK
= becomes VI. This subtraction is memo IJ 22, 2
3 is in the holding state. The output of the subtracter 24 is V
r is truly proportional to the output voltage of the thermocouple 2, and since the offset voltage VOS of the amplifier 4 is removed, a correct measurement value can be obtained.

In the above embodiment, a series body consisting of the analog switch 18 and the resistor 19 was used, but this connects the (+) terminal of the amplifier 4 through the resistor 19 whose resistance value is equal to the internal resistance value of the thermocouple 2. By grounding, the influence of the offset voltage generated by the input offset current of the amplifier 4 is made equal between the state of the first set and the second state, thereby making the effects of the present invention completely complete. However, since the thermocouple 2 has a low internal resistance and can be ignored compared to the resistance 5, the resistance 19 can be omitted. Also, amplifier 4
When the analog switch is of a high input resistance type, the input offset current is extremely small, so the same effect can be obtained by omitting the analog switch 18 and using only the resistor 19. In this case, since the resistance value of the resistor 19 becomes a load on the thermocouple 2, it is desirable to set it to a suitably large value.

Also, after converting the output voltage of the amplifier 4 into a deisotal, the CPU
Although memory is held using I2, it is also possible to use all two Sanzor hold circuits to hold memory and perform subtraction using an operational amplifier. Further, although analog switches 17 and 18 (() were used, the same effect can be obtained by using other switch means such as relays.

As described above, in the present invention, the opening/closing is controlled by all the small signal input switches, and the first state in which a normal input is given to the amplifier and the second state in which all inputs of the amplifier are grounded. and two memory means holding the output voltage of the amplifier in the second state, respectively, and the difference between the outputs of these two memory means is obtained, and the offset of the amplifier Capable of removing voltage automatically.

Therefore, it is possible to eliminate factors that hinder productivity, such as adjusting the initial tolerances of the amplifier, and to obtain accurate measured values without any problems even if the offset voltage varies depending on the environmental temperature. For this reason, we have started using a temperature control device to protect the exhaust gas purification catalyst from overheating, which is often used near its limit temperature.
4 for other systems that handle the output voltage of thermocouples, such as regeneration combustion systems for f-ticulate capture filters in diesel engines? Even if it is (it has a bloody great effect).

It can also be effectively applied to devices that apply a minute voltage, such as an oxygen sensor on the fuel side.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional device, Fig. 2 is a block diagram of a device of the present invention, and Fig. 3 is a functional block diagram for explaining the operation of a CPU according to the present invention.・Thermocouple, 4...Amplifier, 11...A/D converter, l2...CPU, 16...Representation device, 1
7.18... Analog switch, 19... Resistor, 2
2, 23...Memory, 24...Subtractor, 25...
control block. Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Shin Kuzuno −

Claims (1)

[Claims] +11 A first switch means having one end connected to an automobile motion/horizon meter detector to open and close its output, one end connected to the other end of the first switch means and the other a second switch means or a resistor whose end is connected to the reference level of the detector, or a series connection of the second switch means and a resistor; an amplification means whose input side is connected to the other end of the first switch means; A control means for opening and closing the first and second switch means (if present), and an amplifying means when the first switch means is conductive and the second switch means (if present) is cut-off. a storage means for storing the output;
, a second storage means for storing the output of the amplification means when the first switch means is in the cut-off state and the second switch means (if present) is in the conduction state, and the first and second storage means store the output. A micro signal measuring device characterized by being fully equipped with arithmetic means for outputting the difference in content. (2) The amplification means includes an A/D converter, and each storage means is composed of a digital memory, and the amplification means performs a deisotal operation x. A device for measuring minute signals.